Many examples of using arrays of tunable filters (TFA) for add/drop function of OADMs, such as reconfigurable OADMs (ROADMs). So-called “colorless” drop function of ROADM (dropping a group of multiplexed channels and further filtering them by a number of tunable filters) are often implemented by TFA, and it can be seen in two prior art examples shown in FIGS. 1 and 2. However, reconfigurable through channels have been implemented by now by a wavelength blocker or a wavelength selective switch WSS. Together, the TFA units and WSS or blockers implement reconfigurable colorless ROADM. Another example of implementing through/express channels in ROADM is using a separate TFA unit for that. Such ways of implementing ROADM are described in US2009/0226168 A1.
US2009180779 describes an embodiment implementing ROADM by utilizing a TFA for an add-drop module. In another embodiment, at least two ROADMs and at least one add/drop module may further include express ports, wherein the number of express ports is a function of the number of ROADMs and add/drop modules.
However, to the best of the Applicant's knowledge, nobody have supposed that implementation of add/drop and through functions of OADM could be done in a more economic way, so as to solve well known problems of organizing optical channels in modern switching optical equipment.